The spontaneous generation of deleterious unwanted foam during the handling and application of polymeric latices to form a film upon a substrate has been recognized to lead to imperfections and concomitant nonuniformity in the resulting coating. Accordingly, it has been a common practice to also include a defoaming agent in such latices often in a substantial concentration. However, such defoaming agents have often been found to interfere with the wetting and coverage of the surface of the substrate by the latex composition and thereby to interfere with the formation of the desired continuous and uniform polymeric film upon the substrate once the water component is volatilized. It further has been a common practice to seek to remedy this deficiency in surface wetting and coverage through the further inclusion in the latex composition of an anionic surfactant. However, such anionic surfactants have been found commonly to increase the overall foaming propensity of the latex composition and to nevertheless contribute to the nonuniformity of the resulting film in spite of the best intentions of those seeking to apply a highly uniform polymeric film. It has been observed that such nonuniformity of the resulting polymeric film is particularly troublesome when the substrate that receives the latex composition tends to repel water and possesses a hydrophobic surface.
Commonly, polymeric latices are exposed to agitation or other high shear conditions at some point during handling and/or during application to a substrate (e.g., by spraying or the use of high speed transfer rolls) prior to the volatilization of the water component. Such conditions can lead to the production of copious quantities of foam that can adversely influence the character of the resulting polymeric film that is applied to a substrate. Where foam bubbles are present, the coverage of the substrate by the polymeric particles present in the latex composition tends to be hindered.
It is an object of the present invention to provide an improved latex composition for use in coating or adhesive end uses that exhibits a superior ability to form a uniform film upon a substrate.
It is an object of the present invention to provide an improved latex composition wherein the polymeric particles are present at a relatively high concentration and there is a good resistance to excessive foaming even if agitation or other high shear conditions are encountered.
It is an object of the present invention to provide an improved latex composition that can be applied to a substrate by spraying in the absence of excessive foaming.
It is an object of the present invention to provide an improved latex composition that has the ability to well wet and cover the surface of a substrate that is to receive a polymeric film to thereby facilitate uniform spreading in the absence of excessive foaming.
It is an object of the present invention to provide an improved latex composition that has the ability to well wet and cover the surface of a hydrophobic substrate that is to receive a polymeric film.
It is an object of the present invention to provide an improved latex composition wherein a defoaming agent is present in a relatively low concentration in conjunction with a relatively low concentration of a specifically defined nonionic surfactant that has been found through empirical research to yield a highly compatible overall composition that makes possible the formation of a substantially uniform film upon a substrate.
It is an object in a preferred embodiment of the present invention to provide an improved latex composition wherein the total surfactant concentration is relatively low and an anionic surfactant is absent.
It is a further object of the present invention to provide a latex composition that is particularly suited for forming a clear polymeric coating on a paper substrate.
It is a further object of the present invention to provide a latex composition that well forms a pressure-sensitive adhesive layer when applied to the surface of a hydrophobic polyester film substrate and the water component is volatilized.
It is another object of the present invention to provide a process for forming a substantially uniform polymeric film on a substrate while utilizing a latex composition in the absence of excessive foaming.
These and other objects and advantages of the presently claimed invention will be apparent to those of ordinary skill in the art from a reading of the following detailed description and appended claims.
Our companion patent application Ser. No. 321,112 (now U.S. Pat. No. 5,525,657) entitled "Improved Latex Composition Employing Specifically Defined Ethylene Oxide/Propylene Oxide Block Copolymer Surfactant and Hydrophobic Defoaming Agent" is being filed concurrently herewith.